1. Field of the Invention
The invention relates to a communication system, more particularly to an apparatus for performing channel estimation in a receiving device.
2. Description of the Related Art
In order to receive signals from a transmitting end correctly, estimation for a transmission channel is usually performed at a receiving end to compensate amplitude and phase of the received signal caused by the channel so as to correctly receive data. A conventional estimating method is to utilize a decision-feedback technique to determine a decision signal of recovered data, and to obtain channel characteristics by training. However, during the training process, decision errors produced by the decision-feedback, technique will accumulate, so that the result of channel estimation is not correct.
Another conventional estimating method is to insert a pilot signal into a signal at the transmitting end and then estimate characteristics of a channel at the receiving end based on the extent the pilot signal are affected by the channel. For instance, in some single-carrier communication systems, the pilot signal is inserted before the data to be transmitted in the time domain. In some multi-carrier communication systems, the pilot signal is distributed among the data to be transmitted in the frequency domain, e.g., a digital video broadcasting-terrestrial (DVB-T).
However, pilot signals have a profound effect on the accuracy of channel estimation, and the smaller the number of pilot signals, the poorer will be the estimation accuracy. For example, the pseudo noise (PN) sequence is used as pilot signal. Because the number of taps of the PN sequence is insufficient, auto-correlation functions cannot completely simulate the ideal delta function, so that errors are generated in the estimated channel impulse response (i.e., time-domain characteristics of the channel).
For prior art relevant to channel estimation, reference can be made to U.S. Pat. No. 7,548,594 and U.S. Pub. No. 20060039488, and to U.S. Pat. No. 6,654,429.